Since the line or lines for fluid transfer must be connected at one end to the ship, which is the moveable structure, and at the other end to the fixed turret around which the ship turns, problems occur in insuring the total security of the fluid transfer connection, in particular during extensive rotations which may involve several turns of the ship in the same direction about the turret.
One possible solution is to provide, on the turret, a swivel joint through which the transferred fluids can flow. However, in view of the relatively high pressures which hydrocarbons in particular can reach during their production, for example, pressures commonly of one hundred bars or more, swivel joint mechanisms are not very reliable, and present numerous problems particularly with respect to sealing.
Further, the gases from petroleum production are often explosive and, when present in the swivel joint, can cause severe accidents where the hoses or conduits also have electrical lines.
Such problems have led to a search for solutions to eliminate the use of swivel joints. These solutions, in view of the very large dimensions of the structures involved and the complex kinematics and motions, have resulted in structures which are both very expensive and relatively difficult to operate.